1. Field of the Invention
The present invention relates to a failure detection system in a propulsion system mounted in an electric vehicle, a hybrid vehicle, etc., having an electric motor as a propulsion system.
2. Description of the Related Art
In recent years, internal combustion engines that directly inject fuel into the cylinder of an engine and serving as propulsion device for automobiles have been developed and commercialized with the goals of protecting the environment and energy reduction. Furthermore, hybrid automobiles that have installed a propulsion system that combines this type of engine and an electrical motor for propulsion have been gaining notice.
One type of such a hybrid vehicle is a parallel hybrid vehicle that uses an electrical motor as an auxiliary driving source to supplement the output of the engine. As disclosed in Japanese Unexamined Patent Application, First Publication, No. Hei 7-123509, in order to satisfy the needs of the driver while at the same time maintaining the remaining charge of the battery, this parallel hybrid vehicle carries out various types of control such as supplementing the output of the engine using the electrical motor during acceleration and charging the battery by regenerative deceleration during deceleration.
FIG. 5 shows the main components of a propulsion system installed in this hybrid vehicle. In this figure, reference numeral 3 is a battery that generates direct current for driving the electric motor M. Reference numeral 200 is an inverter that converts the direct current supplied from the battery 3 into three-phase alternating current, and provides transistors (IGBT) 201, 202, 203, 204, 205, and 206 whose currents are controlled by signals UL, UH, VL, VH, WL, and WH from a controller 800, described below.
Here, the transistors 201 and 202 are cooperatively conduction controlled by signals UL and UH, and the U-phase of the alternating current is generated from these connection points. In addition, transistors 203 and 204 are cooperatively conduction controlled by signals VL and VH, and the V-phase of the alternating current is generated from these connection points. Furthermore, transistors 205 and 206 are cooperatively conduction controlled by signals WL and WH, and the W-phase of the alternating current is generated from these connection points.
Reference numeral M is, for example, a brushless DC electric motor driven by the three-phase alternating current supplied from the inverter 200, reference symbol S8 is a current sensor that detects the output current of the battery 3, reference symbol S9 is a voltage sensor that detects the output voltage of the battery 10, reference numeral 70 is a magnetic pole position sensor that detects the magnetic pole position of the electric motor 30, and reference numeral 800 is a controller that generates the signals UL, UH, VL, VH, WL, and WH that provide drive control of the inverter 200 based on the signals from each sensor.
In the following explanations, the inverter 200 and the control systems such as the controller 800 for providing drive control of the electric motor M are called the xe2x80x9cmotor control systemxe2x80x9d.
Below, the control operation of the electric motor M by this motor control system is explained.
In the case that the electric motor M is driven by a voltage input, the controller 800 that serves as the motor control system carries out torque control of the electric motor M. That is, the controller 800 inputs each of the signals from the voltage sensor S9, the current sensor S8, and the magnetic pole position sensor 70, and monitors the current and voltage supplied from the battery 3 along with the number of revolutions of electric motor M. In addition, according to an externally given target torque and the number of revolutions of the electric motor M, the target current that should be supplied from the battery 3 is found, and each of the voltage values of the signals UL, UH, VL, VH, WL, and WH output to the inverter 200 are controlled so that the product of the current and voltage monitored (that is, the electrical power) agrees with the target electrical power. Thereby, as a result of control of the current (that is, each of the phase currents) flowing through each transistor in inverter 200, torque control is carried out so that the output torque of the electric motor M attains the target torque.
However, in the system described above, in spite of being subject to severe quality control during manufacture, each part gradually deteriorates over time due to long use, and when the service life has passed, there are cases when there is the occurrence of failure of the type that any one of the phase currents supplied to the electrical motor M becomes obstructed. An example of this failure is the case in which the conduction condition of the gate drive line 810 for supplying the signals from the controller 800 to the gate of the inverter 200 and the three-phase line 210 for supplying three-phase alternating current to the electric motor M from the inverter 200 become defective and short out. Additional examples of possible failure are the conduction of the transistors that form the inverter 200 becoming defective, the windings of the electric motor M being broken, and the magnetic strength of the permanent magnets in the electric motor M attenuating.
Here, in the above-described propulsion system, when there is the occurrence of failure such as the obstruction of the U phase of the current supplied to the electric motor M, according to the above-described motor control system, because the remaining V phase and W phase of the current are increased in order to generate the target torque when the U phase of the current is obstructed, each of the current values of the V phase and the W phase rise abnormally. When this type of torque control is carried out, a large change in the output torque of the electric motor M does not appear, and thus there is the problem that frequently the driver of the vehicle will not notice this failure. In addition, there is also the problem that if this type of failure is left as is over a long time period, the chance of failure due to the abnormal rise in current supplied to the electric motor 30 will increase.
In consideration of the above-described problems, an object of the present invention is to provide a failure detection system for a propulsion system that detects the occurrence of failure such as obstruction of the currents supplied to the electric motor for propulsion in the drive system of, for example, an electric automobile or a hybrid vehicle.
In order to achieve that above-described objects, the present invention has the following structure.
According to this invention, failure detection system in a propulsion system having an electric motor (an essential component corresponding for example to electric motor M described below) as a drive device that drives the vehicle and a motor control system (an essential component corresponding for example to the battery 3, the torque control processing circuit 101, the inverter 200, the current sensor S8, and the voltage sensor S9 described below) that drives this electric motor by supplying polyphase current to it, wherein each of the phase currents of the polyphase current is changed such that the output torque of this electric motor attains the target torque that this electric motor should generate, and provides an abnormal rise in current detection device (an essential component corresponding for example to the current sensor S10, the current limit value calculation circuit 103, and the comparator 104 described below) that detects an abnormal rise in current in any of the phases of this polyphase current and a failure identification device (an essential component corresponding for example to the counter 105 and the failure identification processor (steps S1xcx9cS4 described below) that identifies failure based on the frequency of occurrence of abnormally rising current detected by the abnormal rise in current detection device, and wherein the occurrence of failure that obstructs any one of the current phases supplied to the electric motor for propulsion by carrying out failure identification by detecting an abnormal rise in current occurring in the phase currents supplied to the electric motor.
Specifically, according to this invention, the motor control system controls each of the phase currents so that the electric motor generates the target torque. Here, when failure occurs that obstructs a certain phase current among the polyphase currents supplied to the motor, this phase current decreases and the output torque of the electric motor falls below the target torque. At this time, the motor control system acts so as to maintain the output torque of the electric motor at the target torque by increasing the other phase currents. As a result, the other phase currents rise abnormally. Therefore, when this abnormal rise in current is detected, the occurrence of failure can be detected. In addition, there are rare cases in which this abnormal rise in a phase current is caused by factors other than failure, such as noise, but according to this invention, failure is identified by recognizing an abnormal rise in current generated due to failure based on the frequency of the occurrence of the abnormally high current.
In addition, the abnormal rise in current detection device described above is characterized in providing a current sensor (an essential component corresponding for example to the current sensor S10 described below) that detects respectively each of the phase currents of the polyphase current supplied to the electric motor from the motor control system, a reference value calculation circuit (an essential component corresponding for example to the current limit value calculation circuit 103 described below) that calculates the reference value (an element corresponding to the current limit value 103 described below) giving the reference for detecting the abnormally high current, and a comparator (an essential element corresponding to the comparator 104 described below) that compares the value of each of the phase currents detected by the current sensor and this reference value.
According to this structure, the abnormal rise in current is detected by comparing the value of each of the phase currents of the electric motor detected by the current sensor to a reference value that gives the reference for detection of the abnormal the current. Here, for example, the reference current value is set between the maximum value that each of the phase currents establishes when no phase current is obstructed and the minimum value that phase currents establish when another phase current is obstructed.
Furthermore, the failure identification device is characterized in having a counter (an essential component corresponding for example to the counter 105 described below) that counts the frequency of the occurrence of abnormal rise in current based on the result of the comparison by the comparators and failure is identified to have occurred (a function corresponding to steps S1 to S4 executed by the failure identification processor described below) when the counter value of this counter significantly exceeds the number of the occurrences of abnormal rise in current that would occur by chance in each of the phase currents supplied to the electric motor.
According to this structure, the number of occurrences of abnormal rises in current detected by the abnormal rise in current detection device is counted, and in the case that this count value significantly exceeds the frequency of the occurrence of abnormal rises in current that would occur by chance, the occurrence of failure is detected. Thus, even when abnormal rises in current occur due to chance factors other than failure, there is no identification of the occurrence of failure, and false identifications related to the occurrence of failure can be avoided.
Furthermore, a current limiter circuit (an essential component corresponding for example to the current limiter circuit 102 explained below) that limits each of the phase currents supplied to the electric motor based on the results of comparison by the comparator is provided.
According to this structure, when a phase current supplied to the electric motor rises abnormally, this phase current is limited. Therefore, if the amount of the limit of this phase current is appropriately set, even when there is an abnormal rise in current flow, the failure due to the rise in this phase current does not spread. That is, in the case that failure occurs that is due to an obstruction of a phase current, another phase current is raised so that the output torque of the electric motor attains the target torque, but as a result, there are cases in which an excessive current flows to the electric motor, and the failure spreads. Thus, when an abnormal rise in current occurs, the current limiter circuit inhibited the occurrence of an excessive current that could spread the failure.
Moreover, in this invention, xe2x80x9crise in currentxe2x80x9d device an increase in the absolute value of the current. Therefore, the concept of xe2x80x9crise in currentxe2x80x9d naturally includes the case that the current increases in the positive direction, but also includes an increase in the negative direction.